Field of the Invention
The present invention relates to a manufacturing method of a honeycomb structure forming die, and the honeycomb structure forming die. More particularly, the present invention relates to a manufacturing method of a honeycomb structure forming die in which it is possible to manufacture the honeycomb structure forming die excellent in dimensional accuracy at low manufacturing cost and in short time, and it also relates to the honeycomb structure forming die excellent in dimensional accuracy.
Description of the Related Art
In recent years, there has been the tendency to worldwide strengthen regulations on removal of particulate matter (soot or the like) or toxic substances included in an exhaust gas emitted from an internal combustion engine, a boiler or the like. Attention is attracted to honeycomb structures as a filter to remove the particulate matter and the toxic substances from the exhaust gas, and a catalyst carrier, and there have been suggested a large variety of exhaust gas purification systems including the honeycomb structure. In the above honeycomb structure, for example, porous partition walls define a plurality of cells which become through channels for fluid, and the exhaust gas is purified by the porous partition walls, a catalyst loaded onto the partition walls, and the like.
The honeycomb structure can be manufactured by, for example, extruding a kneaded material by use of an extruder to which a honeycomb structure forming die is attached. Hereinafter, the honeycomb structure forming die will be referred to simply as “the die” sometimes. In this die, back holes to introduce the kneaded material and slits communicating with the back holes are formed in a die substrate made of a pure metal, an alloy or the like. Hereinafter, “the back hole” will be referred to “an introducing hole” sometimes. The slit has a shape which is complementary to “a cell sectional shape” of a honeycomb formed body of a precursor of the honeycomb structure, and has a width corresponding to a thickness of partition walls of the honeycomb formed body. In many cases, a diameter of the back hole is larger than the width of the slit and the back hole is disposed at a position at which the slits intersect. According to the extrusion using this die, the kneaded material introduced from the back holes move to the slits having the narrower width, and is extruded from the slits and discharged as the honeycomb formed body. Further, when the honeycomb formed body is fired, the honeycomb structure is obtainable.
Here, for the purposes of decrease of an initial pressure loss of the honeycomb structure, decrease of a pressure loss when particulate matter is deposited, improvement of thermal shock resistance, improvement of durability, and the like, a shape of cells formed in the honeycomb structure becomes complicated. Here, the shape of the cells means the shape of the cells in a cross section of the honeycomb structure which is perpendicular to a cell extending direction thereof. Hereinafter, the shape of the cells will be referred to as “the cell shape” sometimes. As described above, the honeycomb structure is often prepared by the extrusion, and as the cell shape of the honeycomb structure becomes complicated, the shape of the slits formed in the die for use in preparing the honeycomb structure also becomes complicated. In general, the die is often made of cemented carbide or the like to decrease wear due to use. For the purpose of processing the slits having a fine width into a desirable shape in the die substrate made of cemented carbide having a high wear resistance, a high processing technology is required, and manufacturing of the die might require much manufacturing cost and long time. In the die, the slits through which the kneaded material is extruded to form the partition walls are formed by grind processing with a grinding wheel or the like, wire discharge processing, or discharge processing using electrodes made of a dischargeable material such as a copper-tungsten alloy or carbon graphite (e.g., Patent Documents 1 to 3).
[Patent Document 1] JP-A-2010-131872
[Patent Document 2] JP-A-2011-194537
[Patent Document 3] JP-A-2012-125883